1. Field of the Invention
The present invention relates to an airbag apparatus provided with an airbag whose internal pressure at inflation is controllable.
2. Description of Related Art
An airbag apparatus is known from U.S. Pat. No. 6,648,371: the apparatus has an airbag provided with an exhaust hole for discharging part of inflation gas and a flap element joined to an open/close controller for opening and closing the exhaust hole. By controlling the opening and closing operations of the exhaust hole in accordance with the position or size of an occupant, the internal pressure of airbag is controlled upon inflation.
In this airbag apparatus, the flap element is formed of a flexible sheet-shaped member having a size capable of closing the exhaust hole. The flap element is joined to the open/close controller disposed proximate an inlet port of the airbag, and also to the periphery of the exhaust hole in the outer side of airbag which periphery is in a side apart from the open/close controller. The flap element is adapted to keep closing the exhaust hole when retained by the open/close controller, whereas open up to expose the exhaust hole due to the pressure of inflation gas when released from the open/close controller.
However, since the airbag apparatus includes only one flap element for opening and closing the exhaust hole, the flap element has to be sewn up to the airbag at more region other than the side facing away from the open/close controller for enhancing the sealing property when closing the exhaust hole. A patch or flap element shown in FIG. 5 of the above reference, for example, is sewn up to the periphery of a vent hole or exhaust hole also at the side closer to the open/close controller. A patch element shown in FIG. 6 is sewn up to the airbag at three sides around a plurality of vent holes except the side closest to the open/close controller. With these arrangements, if the flap element is released from the open/close controller upon airbag inflation, the vent hole is exposed only when a sewing yarn joining the flap element and the airbag is torn to separate the flap element and the airbag. That is, the sewing yarn has to be securely torn in order to open the exhaust hole.
In the prior art, moreover, the patch element in FIG. 5 has a size capable of passing through the vent hole. With this arrangement, if the patch element is retained by the open/close controller upon airbag inflation, the airbag inflates while the patch element closes the vent hole. However, if the patch element fails to securely seal the vent hole, inflation gas may leak from a gap between the vent hole and the patch element. For this reason, the apparatus has required a separate means for securely closing the vent hole to prevent gas leakage from the vicinity of the vent hole. In order to secure a stable closed condition of the vent hole it is alternatively contemplated to reduce the size of the vent hole, but a small-sized vent hole cannot discharge enough inflation gas.